1. Field of the Invention
This invention relates to chew toys for domestic animals. In one of its aspects, the invention relates to chew toys that have improved degradability. In another of its aspects, the invention relates to a chew toy made of rawhide that retains the toughness and ‘chewability’ of conventional rawhide chews, thus satisfying the animal's instinctive need to chew, with improved degradability
2. Description of the Related Art
Products for consumption by pets can be evaluated based on a number of characteristics, including entertainment value, chew resistance, toughness, longevity, degradability, nutritional value, and in some cases digestibility, which is related in part to nutritional value. As used herein, digestibility of a substance is defined as a measure of how well the substance is absorbed by the animal's body. Degradability is defined as a measure of how quickly and completely a substance breaks down in the animal's digestive system.
Using these characteristics, products made for pet consumption can generally be classified into two categories. The first category includes food and treats that provide nutritional value to the animal. These products are highly digestible and degradable due to their structural characteristics, but are consumed quickly and do very little to entertain the animal or to satisfy the animal's instinctive need to chew. While they may provide some dental benefits when supplemented with specialized enzymes or other additives, they provide very little mechanical action to clean the teeth or stimulate the gums. The second category includes chew toys and chew resistant articles that provide the ‘chewability’ needed to satisfy the animal's need to chew, and provide the dental benefits and entertainment value that the food and treats of the first category lack. These products are typically made of rawhide pieces which have little or no food value and do not add calories to the animal's diet. These pieces are eventually broken down into small pieces that may be swallowed by the animal and passed through the digestive system of the animal.
A process of making chew toys from untanned bovine skin (rawhide) is well known. In this process, the cattle hides are received from the slaughterhouse with blood, tallow, and flesh on them. The hides are washed and de-haired. De-hairing is achieved chemically using lime and sulfite. Soda ash may also be used in the de-hairing step as a degreaser. The de-hairing process may also employ the use of enzymes that break down creatine to aid hair removal. After de-hairing, the flesh and excess fat is removed and the hides are split into two layers. The top layer is known as the top grain layer. This layer is often tanned and used for footwear, belts, leather, and apparel. The bottom layer is known as the split layer and is the layer commonly used to make articles like suede, gelatin, collagen and chew toys. In the conventional process, untanned rawhide (either top grain or split layer) is further processed using salt, sulfate, and degreaser. The hides may then be bleached with hydrogen peroxide and treated with titanium dioxide before being formed into shaped chew toys and dried.
With a conventional rawhide chew toy, if the dose is not controlled, for example an animal is given too much rawhide, there may be a build-up of rawhide in the animal's digestive system due to the lack of degradability of the rawhide. The build-up of rawhide in the animal's digestive system can cause digestive distress or discomfort to the animal and can sometimes require veterinary care.
One proposed solution to this problem is to break up the rawhide and incorporate it into pet treats or pet food products to make them more chewable. The breakdown of the hide can be achieved mechanically, through the use of chemical processes using enzymes as catalysts, or by using a combination of mechanical and chemical processes. U.S. Pat. No. 4,364,925 to Fisher discloses methods for preparing fibrous collagens from hides by treating comminuted hides with dilute acid in the presence of a proteolytic enzyme. The collagen is then incorporated into a molded pet food product and hardened. Similarly, U.S. Pat. No. 4,145,447 to Fisher et al. discloses compacting wetted animal food under pressure with fibers, such as collagen fibers, and baking the product to form a chew-resistant dog treat. U.S. Pub. No. 2008/0003270 to Garcia Martinez and U.S. Pub. No. 2008/0122133 to Zheng disclose additional methods for mechanically breaking the collagen fibers (through milling or grinding), treating them with solutions including enzymes, and reconstituting the product into chewable dog treats.
GB 929137 to Nihon Hikaru Kabushiki Kaisha discloses a method of using enzyme treatments and acid extraction to solubilize collagen fibers in the skin of adult animals. The method produces a colloidal solution of insoluble collagen fibers in a fiber-reproducible state. The solution is then treated with an alkali to reproduce the collagen fibers. Treats and food products that are produced using these processes are more chew-resistant than conventional treats in that they are harder and require more pressure to break. However, because the collagen fibers are mechanically broken, they lack the toughness and ‘chewability’ of rawhide products. As a result, these products are consumed more quickly by the animal, do not provide the dental benefits of rawhide, and do not satisfy the dog's proclivity for chewing.
To address these issues, pigskins, which are more digestible to animals than rawhide, have been used as a substitute for rawhide for making chew toys. U.S. Pat. No. 6,827,041 to Hague et al. discloses a method of processing pigskins for use in chew toys and treats in which the pigskins are treated with an alkali paste and washed with a pancreatic enzyme to soften the skins. Similarly, U.S. Pub. No. 2007/0292484 to Levin discloses a method that includes treating pigskin with an alkali and enzyme mixture to dissolve the colloidal protein to prepare the pigskin for use in making pet treats. While pigskin products are more digestible than rawhide products, they are more expensive to produce and tend to be thinner and softer than rawhide. As a result, they do not have the chewability of rawhide made from bovine hides and thus do not provide the chew resistance and as much tartar control as bovine rawhide.
U.S. Pat. No. 6,223,693 to Perlberg et al. discloses a process for soaking untanned animal hides in a humectant to produce a softer rawhide product. While this product makes the rawhide softer and easier for older animals to chew, it has no affect on the collagen fibers themselves and, for that reason, it fails to improve the degradability of the rawhide in the animal's digestive tract.
Still other alternatives involve the addition of enzymes to traditional pet foods or treats to provide additional functionality when the product is consumed. U.S. Pat. No. 5,310,541 to Montgomery discloses a chewable and consumable composition that contains a compound which, when it comes into contact with saliva, forms an antimicrobial agent. The preferred carrier is described as rawhide. Similarly, U.S. Pub. No. 2007/0148104 Goettert et al. discloses a pet article (which can include rawhide or biscuits) that improves the dental health of animals. The article can comprise an edible chew base and effective levels of antimicrobial compositions. In one embodiment, the use of a therapeutic enzyme that decomposes harmful carbohydrates, proteins, lipids and bacterial substrates in the pet's mouth is disclosed. In addition, U.S. Pat. No. 7,691,426 to Axelrod et al. discloses a chew toy which incorporates an edible resin and rawhide. The edible resin composition may include starch, gluten, vegetable based protein, carbohydrate or fat based products that supplement the animal's nutritional feeding regime. The resin may include enzymes and/or co-enzymes. While these types of alternatives may improve the dental or nutritional benefits of pet treats, they do not provide a safe, degradable, chew toy while maintaining the ‘chewability,’ mechanical teeth-cleaning action, and extended chewability of rawhide.
Methods have also been disclosed for producing artificial rawhide. U.S. Pub. No. 2004/0187794 to Nakata discloses a method of making artificial rawhide to improve the efficiency and cost-effectiveness of the dog chew process. The natural rawhide is decomposed, either mechanically or with the help of an enzyme. The collagen fibers are then blended with a binder and water and extruded to form a sheet of artificial rawhide.
It is well known in the art that enzymes are used for various purposes during the tanning process. U.S. Pat. No. 4,968,621 to Pfleiderer et al. discloses a process for the wet degreasing of hides using enzymes, also called bating, which is also carried out in the presence of synthetic surfactants. U.S. Pat. No. 5,710,040 to Christner et al. discloses that proteolytic enzymes can be used to more quickly rehydrate the skins that are delivered dry and to more completely degrease the skins and also, after soaking, to provide a smoother, cleaner, and softer hide. Proteases also support loosening of the hair from the skin. U.S. Pat. No. 4,614,520 to Ibello et al. also discloses the use of enzymes as part of a bating step after liming to soften the hides. U.S. Pat. No. 4,457,759 to Fekete et al. discloses a process for treating hides which includes the use of enzymes in de-hairing. Enzyme use for removal of hair is further disclosed in U.S. Pat. No. 6,957,554 to Saravanabhavan et al., U.S. Pat. No. 3,939,040 to Monsheimer et al., U.S. Pat. No. 6,708,531 to Thanikaivelan et al., and U.S. Pat. No. 5,834,299 to Andersen. Finally, U.S. Pat. No. 5,670,369 to Fink et al. discloses that it is known to use enzymes to treat hides to solubilize collagen, which can then be extracted and used for purposes such as medical implants.